When an underground pipe, such as pipelines and passageways, becomes defective or too old to perform properly, the pipe is repaired and rehabilitated without digging the earth to expose the pipe and disassembling the sections of the pipe. This non-digging method of repairing an underground pipe has been known and practiced commonly in the field of civil engineering. Typically, the method is disclosed by Japanese Provisional Patent Publication (Kokai) No. 60-242038.
According to this publication, this method of pipe repair comprises inserting a sufficiently long tubular flexible liner bag into the pipe to be repaired by means of a pressurized fluid, like air and water. The tubular liner bag is made of a flexible resin-absorbent material impregnated with a thermosetting resin, and has the outer surface covered with an impermeable plastic film.
More particularly, according to the publication, the tubular flexible liner bag is closed at one end and open at the other; the tubular flexible liner bag is first flattened, then, the closed end of the tubular liner bag is tied to a control rope; the open end of the tubular liner bag is made to gape wide and hooked (anchored) at the end of the defective or old pipe in a manner such that the wide-opened end of the liner completely and fixedly covers and closes the pipe end; a portion of the liner is pushed into the pipe; then, the pressurized fluid is applied to the said portion of the tubular liner such that the fluid urges the tubular liner to enter the pipe. Since one end of the tubular liner is hooked at the end of the pipe, it remains there while the rest of the flexible liner bag is turned inside out as it proceeds deeper in the pipe. (Hereinafter, this manner of insertion shall be called "everting".) When the entire length of the tubular liner bag is everted (i.e., turned inside out) into the pipe, the control rope holds the closed end of the tubular liner bag to thereby control the length of the tubular liner in the pipe. Then, the everted tubular liner is pressed against the inner wall of the pipe by the said pressurized fluid, and the tubular flexible liner is hardened as the thermosetting resin impregnated in the liner is heated, which is effected by heating the fluid filling the tubular liner bag by means of a hot steam, etc. It is thus possible to line the inside wall of the defective or old pipe with a rigid liner without digging the ground and disassembling the pipe sections.
When, however, the pipe has a second pipe branching out from it, it is necessary to cut off that portion of the liner which closes the branch pipe. To do so, as shown in FIG. 13, a cutter apparatus having a hole saw type cutter 101 having a diameter corresponding to the size of the branch pipe is conventionally employed, which is brought in the main pipe 115 and operated to bore and cut open the liner 117 at the branch pipe 116. Alternatively, a cutter apparatus having a conical grinding cutter 201, as shown in FIG. 14, is used.
Now, as shown in FIG. 13, which is a vertical sectional view of a sewerage site, the branch pipe 116 is usually tilted in a manner such that the flow of the liquid down the branch pipe 116 acquires a momentum to rush downstream when it enters the main pipe 115. In other words, when the downstream of the main pipe 115 is to the left, the angle .theta. is substantially smaller than 90 degrees. As a result, the end hole of the branch pipe 116 to open into the main pipe 115 has a shape of ellipse rather than a circle, as shown in FIG. 15. Therefore, when the liner 117 is cut open by a hole saw type cutter 101 or by a conical grinding cutter 201, the hole 117a cut open is circular and two burrs 117b of crescent shape (hatched in FIG. 15) are left about the hole 117a to constrict the passage. And the size of the burrs 117b will be greater when the center of the cutter is not suitably positioned with respect to the position of the branch pipe 116.
Furthermore, when the diameter d of the branch pipe 116 is relatively large, a cutter 101 (or 201) is selected which has a comparatively large diameter D, and when the diameter D.sub.1 of the main pipe 115 is not by far larger than the cutter 101, the combined vertical length of the cutter 101 and the motor 123 becomes so great that it is difficult to enter and transport the cutter apparatus into the main pipe without the cutter touching the wall of the main pipe 115; and in this case, the operator who remote-control the cutter 101 must be an experienced skillful one able to accurately move the cutter since the cutter 101 is not allowed to have a large vertical stroke.
Also, as shown in FIG. 14, when the thermosetting resin that has oozed out from the tubular liner 117 gathers and forms a resin pool 130, the cutting operation becomes difficult because the increased friction lowers the cutting speed, and clogging of the saw teeth with the resin decreases the cutting efficiency of the cutter.
In consideration of these problems, there has been contrived a method wherein, as shown in FIG. 16, a thin rod-shaped rotary cutter 301 is used to first puncture the liner at a location close to the inner wall of the branch pipe, and then to move the spinning cutter 301 along the inner edge of the branch pipe 116 to cut open the circular hole (in fact elliptical). However, in practice it is difficult to move the thin rod-shaped rotary cutter 301 to describe a circle or ellipse for such a cutter is so poor in rigidity that it twists and vibrates a good deal and as the result the cutter does not make a clear cut line even when it is monitored by a TV camera 121.
Also, it is possible to adopt a disc-shaped grindstone 401, as shown in FIG. 17, to grind through the liner; however, a locking means 114 such as a nut is necessarily provided on top of the grindstone 401 to lock the grindstone 401 about the rotary shaft 113, and this means 114 gets in the way and prevents grindstone from opening the hole.
Another problem with a conventional cutter is that when it is so worn that its service life is over, it is necessary to entirely replace it with a new one, which is a very costly practice.
Incidentally, the hole making operation on the tubular liner 11, shown in FIG. 13, is conducted by means of a robot 120 (cutter apparatus), whose movement is remote-controlled through monitoring by a TV camera 121 introduced in the main pipe 115.
However, a problem with this system is that the cord 127 connected to the TV camera 121 and the cord 129 connected to the robot 120 tend to get in the way and prevent the TV camera 121 and the robot 120 from moving smoothly.